Process of protective lining and coating of pipes



Patented Dec. 5, 1939 UNITED STATES PROCESS OF PROTECTIVE LINING AND COATING OF PIPES Oscar G. Goldman,

San Francisco, Calif.

No Drawing. Application March 25, 1938,

Serial No. 198,082

3 Claims.

This invention relates to the protection of steel and iron pipes, particularly large water pipes, both inside and outside with bituminous or tar coatings to protect the metal against corrosion,

5 and the object of the invention is to provide an improved process or method of applying the coating and lining.

Before describing the invention it will simplify its understanding to mention that coatings and linings of tar or pitch or asphalt have been applied to iron and steel pipes for many years and they have generally been applied either with liquid or molten tar or asphalt preparations, either swabbed or brushed on, or the pipes have been dipped into tanks of molten tar or asphalt and drained before stacking. Such coatings, however, were uneven, and also covered the ends of the pipes, and the coatings could not be practicably made as thick as required in modern practice.

With the increased use of sheet steel pipe of large diameters which were welded at the joints to form a continuous tube sometimes carrying the main water supply for a city, the ordinary tar or asphalt coat was not suificiently protective, and it was found desirable to build up linings of about inch or more in thickness, also to leave the extreme ends and outer margins bare to facilitate butt welding of the sections together, or lap welding where bell and spigot joints were used.

To apply such heavier linings within the pipes recourse was had to revolving the pipes on a horizontal axis while introducing the molten asphaltic and/or tar or pitch compound so that it would be distributed evenly by centrifugal force. It was also known to use dams or retaining rings at'the ends of the pipe being thus centrifugally lined, so as to accurately determine the thickness of the lining layer produced, as the excess would overflow.

It was also proposed to fill, the asphaltic or tarry matter with an inert material, such as diatomaceous earth, ground sand, granite chips, etc. to give it more body, as set out in United States Patents Nos. 1,555,257 and 1,605,574.

However, it was further found that unless the pipe were hot, such coatings did not adhere perfectly and consequently it became the practice to. first apply a substratum or priming coat of more adherent material, of which proprietory brands have been put on the market, and particularly was this necessary after centrifugal interior lining offa pipe, as it could not be heated to the 55.. te'mp'erature required for efiective outside coating without injury to the lining which would easily slide from any over-heated portions ofthe pipe and which were almost impossible to avoid.

My invention provides a means by which the asphaltic o-r tar coating may be applied both inside and outside of a hot pipe to thereby gain maximum adhesion, yet without the use of a primer or substratum, and it consists essentially of the following steps:

A. The pipes are supported horizontally so that they may be rotated, and preferably by live and idler rollers at the ends of the pipes where the bare margins are desirable. B. Heat is applied to the pipe either exteriorly or interiorly or both by any suitable means, and preferably while the pipe is slowlyrevolving. The pipe should be evenly heated'to about 325 F., or to a temperature between 275 to 325 F. or to apoint well above the softening point of the bituminous or tar coating material used, the preferred range being between about 200 to 400 degrees F. I

C. The heating equipment is either removed or the heat turned off, or down if no naked flame is present, and a coating of the hot molten material is applied to the exterior of the pipe while it is revolving (preferably at about eight or nine R. P.- M. for a sixty inch diameter pipe), either by means of swabs, brushes, pouring it on, or feeding it onto the pipe from a trough of liquid or molten coating material.

D. This exterior coating must be relatively thin so that it will not be thrown off by centrifugal force when the pipe is speeded up for the next operation, and it should be quickly applied before the pipe has materially cooled, and being thin,

will set in a moment in contact with the hot pipe.

E. The pipe is now speeded-up (to about seventy-two R. P. M. or more for a sixty inch diameter pipe) and the interior lining is applied by pouring in the molten material generally at about four or five hundred degrees Fahrenheit, and leveling it off until by the efiect of centrifugal force it builds up to the desired thickness. End dams or retaining rings may be used, or if the lining material is stabilized or of the type set out in the above mentioned patents, it can be-satisfactorily applied without dam rings.

F. As soon as the proper thickness is secured the pipe is cooled somewhat either by cool air being forced through it or water sprinkled on its exterior and/or interior, all while the pipe continues to revolve till the interior lining is firmly set. During this internal lining operation heat may be applied to the already thinly coated exterior surface if desired, especially in cold weather, if it be done with care not to burn orexcessively heat the exterior coating.

G. The pipe is slowed down again and preferably while still warm the outer layer is built up to the required thickness by further application of the molten material in any'of the manners described, or it may be spirally wrapped in tar or asphalt impregnated asbestos felt, or other approved wrapping, with simultaneous application It should be noted that were the first thin outer coat not applied to a heated pipe, it would not make the required bond but would require the use of a substratum or primer. Also to be noted is that were a pipe centrifugally lined interiorly only as disclosed in the two prior patents men- 'tioned. an outer coating of bitumen or tar would not thereafter secure a proper bond without the use of a primer, as the pipe could not again be heated on account of the thick interior coating in place which would melt and slide. But by following my improved method as described, the thin first exterior coat being applied hot or liquid to a hot pipe insures a bond and quick setting to prevent throwing off when the pipe is speeded upfor the interior lining, while the interior centrifugally placed lining is also bonded for the same reason, and the subsequent building up of the outer coat, though applied to a cooled or almost cooled pipe will nevertheless bond perfectly, asit is applied to a previous heat bonded layer of the same type of material, and it is these novel cooperating steps of procedure which constitutes my improved proc ess as it permits at least twice the amount of pipe to be properly coated inside and out with a given crew in a given time, and entirelyeliminates the requirement of a ,coat of primer, as the asphalt, or tar is applied to the bare metal.

In my appended claims the word bituminous is intended to include any coating materials containing asphalt, tar, coal tar, or pitch or enamel, or admixtures, and whether filled or not.

Electric welding is preferred for joining the I therefore claim:

1. The process of applying protective coatings to metal pipes which comprises applying a relatively thin coating of hot liquid bituminous material to the outer side of a hot pipe while slowly revolving the pipe on a horizontal axis at a speed insufiicient to throw oil the material and until the thin coating has set, then increasing the speed of revolution of the pipe and applying to the still hot pipe a relatively thick internal lining of a hot molten bituminous material and continuing the fast rotation of the pipe until the internal layer is even and in set condition, thereafter slowing down the rotary motion of the pipe again and building up the outer coating to the required thickness by further application of a hot molten bituminous material to the outside of the still warm pipe.

2. The process of applying protective coatings to metal pipes which comprises rotating a pipe on a horizontal axis and heating the pipe, then while the hot pipe is revolving at a speed insufficient to throw off the material applying a thin coat of hot molten bituminous material to the exterior wall of the pipe, then when sufiiciently set speeding up the rotation and applying a thick layer of hot molten bituminous material to the interior of the pipe for smoothing out by centrifugal action, setting the internal layer, slowing down the rotary speed of the pipe and build- -ing up the thickness of the external layer of bituminous material by further application of the hot molten bituminous material while the pipe is slowly revolving. I

3. The process of applying protective coatings to metal pipes which comprises rotating a pipe on a horizontal axis while applying heat to bring the temperature of the pipe to a point between about 200 to 400 degrees F., then while the hot pipe is revolving at a speed insuflicient to throw oil the material applying a thin quick setting coat of hot molten bituminous material to the exterior wall of the pipe, then when sufliciently set speeding up the rotation and applying a thick layer of molten bituminous material to the interior -of the pipe for smoothing out by centrifugal action, setting the internal layer by the application thereto of a cooling fluid, slowing down the rotary speed of the pipe and building up the thickness of the external layer of bituminous material by further application of the hot molten material while the pipe is slowly revolving.

OSCAR G. GOLDMAN. 

